Automatic telephone system



May 27, 1930. R. G. RICHARDSON AUTOMATIC TELEPHONE SYSTEM Filed April 8, I926 Sheets-Sheet 1 Inusn nz" Racine EE'mhardsun M g, EU?

May 27, 1930. R. G. RICHARDSON AUTOMATIC TELEPHONE SYSTEM" Filed April 8, ,1926

2 Sheets-Sheet 2 usn cm E. Ezchardsnn Q Em Rudns Patented May 27, 1930 RODNEY G. RICHARDSON, OF CHICAGO, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNMENTS,

T AUTOMATIC ELECTRIC INC, OF CHICAGO, ILLINOIS, A CORYORATION OF DELA- WARE AUTOMATIC TELEPHONE SYSTEM Application filed April 8, 1926. Serial No. 100,494.

This invention relates to automatic telephone systems in general, but is more particularly concerned with automatic telephone systems which include private branch exchanges. In such a system, each private branch exchange, which may be either a manual or an automatic branch exchange may have a plurality of trunks extending to a main automatic exchange, the number of trunks in each case depending on the size of the private branch exchange. According to the usual practice, a single telephone number is assigned to each private branch exchange, and when a subscriber at an automatic substation desires a connection with a certain private branch exchange, he operates his calling device in accordance with the number of that branch exchange. In response thereto, automatic switches at the automatic exchange operate to extend the desired connection to that private branch exchange.

This invention is not peculiar to any particular kind of automatic system, but in this embodiment of the invention it will be assumed that Strowger automatic switches are employed. In such a system the last switch to be operated responsive to digits dialed by a calling subscriber in extending a connection to a branch exchange usually is a rotary connector in whose banks the trunks from various private branch exchanges terminate. A rotary connector operates responsive to the last two digits dialed to select the group of trunks extending to the desired exchange, and then automatically selects an idle one of these trunks. As many trunks as may be needed to carry the traffic are assigned to each private branch exchange (abbreviated P. B. X.) to which service is rendered. For example, four trunks may be needed to carry the traliic to the P. B. X. A. The first four trunks in the second level may be assigned to the P. B. X. A. The remaining six trunks in this level may be assigned to the P. B. X. B. The last two digits in the directory being the number of the first trunk of the group of four. The last two digits in the directory number of P. B. X. B are 25, being the number of the firsttrunk of the group of six. I

In the above example, the numbers of the other eight trunks in the second level cannot be used as telephone numbers and are therefore wasted. In general, then as many telephone numbers are used up for each P. B. X. as there are trunks extending to that P. B. X., although only one number is actually required. The system as briefly described above is therefore verywasteful of numbers, which may become a very serious consideration.

Furthermore, from the above example it is also evident that theP. B. X. A could not be assigned additional trunks to carry an increased amount of trafiic without changing thetelephone number of the P. B. X. A or the P. B. X. B. The same applies to any P. B. X. if there are no unassigned trunk positions in the rotary connector banks adjacent to the last trunk to that P. B. X. Of course, a certain estimated number. of positions adjacent to the last trunk to each P. B. X. can be left vacant when telephone numbers and trunks are initially assigned, but this'estimate can neverv be perfect, and

therefore the telephone number of some nectors in whose banks the trunks terminate. The new arrangement thereby accomplishes the following results:

No telephone numbers are wasted. All possible number combinations. may be used for telephone numbers, and a P. B. X. may be assigned a telephone number without regard to the position of the trunks to that P. B. X. in the connector banks, or to the particular connector group in whose banks these trunks appear.

As regardseach individual P. B. X. no provision for future growth need be made; no trunk positions need be left vacant adjacent to the last trunk to a P. B. X.

The number of trunks to a P. B. X. may be increased and their position in the con nector banks may be changed without having to change the telephone number of that P. B. X. or any other P. B. X.

The telephone number of a P. B. X. may be changed without having to change the position of the trunks in the connector banks.

All the foregoing is accomplished without abandoning the well known and reliable rotary connectors, which ha'veproved to be eminently satisfactory for private branch exchange service, except for the disadvantages which are mentioned above and which are overcome by the present invention.

The new arrangement proposed by this invention for accomplishing the above objects and other objects not specifically stated, and the apparatus used, is fully described in the following specification, with reference to the accompanying drawings comprising Figs. 1 and 2. The drawings, when Fig. l is placed above 2 with the lines of the same designation in alignment, show by means of the usual schematic circuit diagrams that part of a telephone system, such as referred to above, to which this invention particularly pertains.

The telephone system concerned may be assumed to be a 10,000 line system. It may further be assumed that there are three groups of rotary connectors, each group having trunks from various P. B. X.s terminating in its banks. In an ordinary system the connectors of each of the three groups would be'accessible in a different level of the banks of second selectors. In the present arrangement, however, the second selectors as regards only one level are divided into as many sub-groups as are necessary to provide trunks to carry the P. B. X. trafilc. Each of these trunks extends to a rotary line switch. Associated with each trunk is a trunk circuit and a register sender selector. Each register sender selector has access to a plurality of register senders. In the banks of the rotary lineswitches one or more groups of special selectors are accessible and the three groups of rotary connectors are each accessible in a different level in the banks of these special selectors.

In Fig. l, the trunk line coming from second selector bank contacts 2, 3, and 4, is one of the above referred to trunk lines ex tending to the rotary lineswitch RLS. Associated with this trunk is the trunk circuit TC comprising various controlling relays, and the register sender selector RSS. The register sender selector comprises the switching relay 30, operating magnet 35, and wipers 37-40, inclusive, which have no normal position and rotate in a forward direction only. In its banks, access is had to a plurality of register senders.

The rotary lineswitch PtLS, indicated only by a rectangle may be of the well known type having no normal position and rotating in a forward direction only, motion being im parted thereto .on the backward stroke of the operating magnet.

The selector S, indicated only by a rectangle, may be of the well known type having a directive vertical movement and an automatic rotary trunk hunting movement. 1

The rotary connector RC, also indicated merely by a rectangle, may be of the well known type having a directive vertical movement, a directive-rotary movement, and an automatic rotary trunk hunting movement. The rotary connector RC is one of a group of connectors accessible in the third level of bank contacts of the special selectors.

In Fig. 2 the register sender is shown which is accessible, by way of the control conductors n n, inclusive, in the banks of the register sender selectors. The register sender comprises the sender switch SS with its controlling relays, the sequence switch SS, an intermediate distributing frame designated I. D. F. and the register It, which is a Strowger switch element consisting of the usual banks of ten rows of contacts of ten sets of contacts each, and the necessary controlling relays and operating and release magnets.

In their mechanical construction and operation, the sender switch SS and the sequence switch SS are like the rotary lineswitch RLS. The bank connections and multipling are clearly indicated in the drawing. It may be mentioned that in practice, the banks of sender switch SS andthe sequence switch SS have the usual number of 25 sets of contacts. To utilize all contacts most efliciently, the contacts shown may be multipled with the respective remaining contacts as is well understood.

To supplement the disclosure herein and in particular to supply circuits not'shown, reference is made to the following: Pat. No. 1,691,410 toNelson et aL, granted Nov. 13, 1928; Pat. No. 1,349,381 to Jacobson, granted Aug. 10,1920; Pat. No. 1,528,? 51 to Bellamy et al., granted Mar. 10, 1925.

The system and apparatus involved having been described, a detailed description of its operation may now be given. For this purpose it may be assumed that 'a subscriber atan automatic substation wishes to establish a connection with a certain subscriber in a certain P. B. X. system. To establish this connection the calling subscriber will remove his receiver and dial the directory number of the P. B. X. serving the desired subs scriber, and alter this connection is completed, the calling subscriber will inform the answ ring operator at the P. B. X. of the desired connection. vThe operator at the P. B. X. will then complete the connection to the desired subscriber in the usual manner.

In response to removal or the receiver atthe calling substation and the dialing of the irst digit, a first selector is operated to engage with an idle trunk to a second selector of the proper group." in response to the dialing of the second digit, this second selector is operated to raise its wipers opposite the proper level of bank contacts, and rotate its wipers to hunt a trunk whose test conductor is ungrounded. In the present disclosure, in addition to the trunks, accessible in the second selector banks, which are actually busy, those trunks whose associated register sender selectors have their wipers positioned on contacts leading to busy register senders are also marked busy by ground potential on their test conductors; This is by reason of the fact that there is a. continuous metallic path from the test wiper 39 to release conductor 3 when the trunk is idle, thereby causing conductor 3 to be grounded when the release conductor engaged by wiper 39 is grounded. Thus, a second selector, in hunting an idle trunk, will select only such idle trunk whose associated register sender selector is connected to an idle register sender. Further explanation of this Feature will be given in later descriptions.

It may be assumed that the trunk accessible in bank contacts 2, 3 and 4 is idle at this time, and further, that the register sender with which th register sender selector RSS is now connected, namely, the register sender shown in Fig. 2, is also idle at this time. No ground potential will be present on bank contact 3, and assuming this is the first contact somarl-t d the wipers of the second selector used will come to rest in engagement with contacts 2, 3 and 4, respectively. When the second selector connects with this trunk,

ground potential is immediately applied to bank contact 3 and release conductor 3 by the second selector to mark the selected trunk engaged. Ground potential is also applied to bank contact 43 and the contacts multipled therewith, from ground on conductor 3, armature' 25 and the resting contact, wiper 39,

to contact .43. The registersender accessible at bank contact-s 41-44, inclusive, is no marked engaged.

l/Vhen the trunk is seized, a circuit is closed which extends over the talking loop to bank contacts 2 and 4, conductors 2 and 4, armatures 22 and 26 and their resting contact-s, through the upper and lower windingsof the line relay 11 to battery and ground, respectively. Line relay 11 operates and closes a circuit for the release relay 12 at armature 15. Release relay 12 operates and supplies ground potential to the release conductor 3-at armature 17, thereby maintaining the guardpotential on the bank contacts multipled vith bank contacts 3 and providing a holding circuit for the previously opera-ted switches, this taking place before the release relay in the second selector has had time to fall back.

In addition to marking the trunk engaged, the placing of ground on conductor 3 .closes an obvious circuit for relay 13. Relay 13 operates, but by reason of its slow-to-pull-u-p characteristic, which characteristic is indicated on the drawing by the solid black portion on the upper end of its core, the opera tion of relay 13 does not take place until after relay 12 has operated. Although a point in the circuit of the magnet 35 of the switch RSS is closed at armature 21, its circuit is open at armature 18at this time. At armature 20 the resistance 27 in the chain circuit for the marginal relay 5 is short circuited. The function of the operation of re lay 13 and of relay 5 will be described more in detail in later paragraphs.

A further result ot'the operation of relay 12 is the closure of the circuit for switching relay 300i switch ESS at armature 19. circuit may be traced from ground on conductor 3, armature 24 and the resting contact, working contact and armature 19, through the winding of relay 30 to battery. In operating, relay 30 connects the seized register sender into operative relation with the trunk circuit TC by performing the tollowing circuit changes: At armature 34 the impulsing circuit for the operating magnets of the register R is prepared, and at armatures 31 and 32, the control conductors 41 and 42 are connected to the trunk conductors 52 and 54, respectively.

. When the register sender was first marl-red engaged by the application otground on the contact 43, a circuit was closed for the release relay 140 by way of conductor 43 connected to the grounded contact 43, through the winding of relay 140 to battery. Relay 140 operates over this circuit and by the disengagement of armature 144 with its resting contact opens a point in the circuit of the release magnet 119 of the register sender, and prepares thelocking-circuit for relay 1'0)? by the engagement of this armature with its working contact. A pointin the returnstep .springs164 and at armature 149 and the resting contact. This bridge, placed across the conductors 52 and 54 by the operation of relay 30 of the switch RSS, initiates the operation of the rotary lineswitch RLS to hunt a trunk to an idle special selector in thewell known manner. It may be assumed that the trunk selected is the one accessible atbank contacts 55,v 56,

and 57 extending to the selector S. The line and the release relays in selector S, by reason of the bridge across the conductors 52 and 54, now connected to selector S by way of wipers 52 and 54, and bank contacts 55 and 57, then operate to prepare'the selector S to receive a first set of impulses sent thereto by the sender switch SS, as will be described later.

In response to'the dialing of the next digit by the calling subscriber, interruptions in the circuit of line relay 11 are produced at the calling station, thereby causing the deenergization and reenergization of the line relay 11 a number of times corresponding to the digit dialled. The first time line relay 11 deenergizes, a ground impulse is sent to the vertical magnet 11'? by way of resting contact and armature 16, armature 34 and the working contact, wiper 40, bank contact 44, impulse conductor .44, normally closed off-normal springs 114, through the winding of the series relay 105, through the winding of the vertical magnet 117 to battery. Vertical magnet 117 operates and raises the wipers 121, 122, and 123 ofthe register B one vertical step. This operation shifts the vertical off-normal springs, opening springs 114 and closing springs 115 and 116. Relay 105 also energizes and operates its armature 108. The remaining impulses of the first digit traverse the same path traced above except that the path now includes the closed springs 115 and armature 108 and the working contact and excludes springs 114. Relay 105 by reason of its slow-acting characteristics is maintained operated during the transmission of impulses to the vertical magnet 117..

In response to these impulses, vertical magnet 117 operates and positions the switch wipers opposite the level of bank contacts of the register R corresponding to the digit dialled. At the termination of this series of impulses, relay 105 deenergizes and prepares a circuit for the rotary magnet 118 at armature 108 and its resting contact.

In response to the dialing of the next digit, line relay 11 again deenergizes and reenergizes a corresponding number of times. A corresponding number of ground impulses are sent to the rotary magnet 118, the path by armature 112, through the winding of the series relay 106, through the Winding of the rotary magnet 118 to battery. Relay 106, also slow to release, operates over this circuit and closes a circuit for relay 107 which may be traced from ground by way of armature 144 and theworking contact, armature 109 and the working contact, through the winding of relay 107 to battery. Relay 107 energizes and closes a locking circuit for itself at armature 111, and at armature 112 alters the impulsing path to include this armature and the working contact, and armature 110 and the working contact. At armature 113 a point in the stepping circuit for thesending switch SS is prepared, this circuit being open at the present time at armature 120. The operation of the rotary magnet 118 causes the wipers 121, 122, and 123 of the register R to engage the set of bank contacts corresponding to the last two digits of the telephone number of the P. B. X. with which connection is desired. 1

The following assumptions may now be made: that five trunks extend to the P. B. X. with which connection is desired; that the group of rotary connectors having access to these trunks to this P. B. X. are accessible in the third level of the special selector banks; and further that these trunks are accessible in the fifth level of the banks of this group of rotary connectors, the first of these trunks terminating in the sixth set of bank contacts in the fifth level. In order to trunk the call to the desired P. B. X. sender switch SS must send out the digits 3, 5, and 6, consecutively. Therefore, on the intermediate distributing frame I. D.F., the terminal connected to the bank contact 133 is cross-connected to the right-hand terminal No. 3; the terminal connected to the bank contact 132 is cross-connected to the right hand terminal No. 5; and the terminal connected to the bank contact 131 is cross-connected to the right-hand terminal No. 6. The common terminals on the righthand side of the I. D. F. are permanently connected to corresponding bank contacts of the sender switch SS as shown. 7

At the termination of the impulses to the rotary magnet 118, series relay 106 deenergizes and'at armature 120 closes the impulsing circuit for the sender switch magnet 160, which may be traced from common ground interrupter I, armature 120 and the resting contact, armature 113 and the working contact,resting contact and armature 147,through the winding of magnet 160 to battery. The interrupter I sends ground impulses over this circuit to the magnet 160 at the predetermined rate at which impulses are to be sent to the succeeding switches. in response to the first ground impulse, magnet 160 energizes and deenergizes, and in deenergizing, armature 159 moves the Wipers 161and 162 of the sender switch SS into engagement with the contacts 171 and 171, respectively. A circuit is thereby closed from ground on bank contact 171, wiper 161, through the i. ding of the piclr-up relay 142 to b At armature 149 the shunt around the iinpulsing springs 164 is removed; at armature 150 a local circuit is closed for the release relay 140 and ground potential is supplied to release conductor 43 to insure the holding of the sender selector until the completion of the transmission of a digit; and at armature 151 the circuit of the sequence switch magnet 101 is closed, which may be traced from ground by way of the working contact and armature 151, armature 148 and the resting contact, through the winding of magnet 101-to battery.

Upon the next energization and deenergization of the magnet 160, the bridge across the control conductors 41 and 42 is opened by separation of the impulsing springs 164. In releasing, armature 159 advances the wipers'161 and 162 into engagement with the next set of bank contacts, namely, banl: contacts 172 and 1'72, respectively. Since the cross connections at the intermediate distributing frame I. D. F., are such as to predetermine the first code digit to be transmitted to be the digit 3, the operation of the stepping magnetv160 continues under the influence of the interrupter 1 until three interruptions have been produced in the bridge across the control conductor .41 and 42 at the impulsing springs 164, the first interruption being produced just prior to and during the movement o1 wipers 161162 from bank contacts 171- 171 to bank contacts 1Z2172 as described above, the second interruption being produced just prior to and during the movement of wipers 161162 from bank contacts 172172 to bank contacts 173-173, the third interruption being produced just prior to and during the movement of Wipers 161162 from bank contacts 173173 to At armature 144 contact the impulsing circuit of magnet 160 IS opened, and at the working contact t ere- L J3 K 1 or the sell-interrupting stepping (31101111? for magnet 160 is closed. At armature 148 and the resting contact, the circuit of the sequence switch magnet 101 is opened and at the workin contacts thereof the temporary locking circuit of stop relay 141 is closed. Magnet .160 now operates in a buzzer like manner over the circuit from ground multiply c011- nected to the bank contacts engaged by wiper 161, interrupting spring 163, working contact and armature 14'? through the winding of the magnet 160 tobattery, thereby advancing the Wipers 161 and 162 back to their normal position, in which position wiper 161 again engages the ungrounded contact 170. The circuit of the pick-up relay 142 is then opened. This relay, being sloW-to-release, retains its armature in an energized posi tion for a short time. Magnet 101, in deenergizing, advances the wipers 102 and 108 into engagement with the second set of con tacts, In response to the three-interruptions in the bridge across the control conductors 41 and 42, the selector S operates in the well known manner to raise its wipers opposite the third level of bank contacts after which selector S performs its automatic rotary movement to hunt a trunk to an idle rotary connector accessible in this level of bank contacts. It may be assumed that the rotary connector RC accessible at the bank contacts 65, 66, 6?, is idle at this time and is the one connected With. In response thereto the line relay and the release relay in the rotary connector l t-C are caused to operate in the Well known manner, thereby preparing rotary connector-RC to. receive the next set of impulses l V hen the pick-up relay 142 releases its ar- I matures, the impulsing springs 164 are again shunted at armature 149, and the temporary locking clrcuit for the stop relay 141 is opened at armature 151. Stop relay 141 is also slowacting and retains its armatures in an operated position for a short interval. after its circuit is opened after, which it releases its armatures. The circuits are then such as to cause the sender switch SS to interrupt the bridge across the control conductors 41 and 42in accordance wi h the next digit to be sent to the rotary'connector RC. The time gained by reason of the sl0W-to-release characteristics of the relays 142 and 141 before the sender switch SS is again operated is sufiicient for the selector S to execute its rotary hunting movement and for the preparation of the rotary connector RC to receive the next set of impulses;

When relay 141 falls back, magnet 160 is again operated'under the influence or the interrupter I to advance the switch wipers 161 and 162 in the manner described above until the wiper 162 as before, engages a grounded Contact, this now being the bank contact 17 5. A circuit is then closed which may be traced from ground by way of wiper 103 which is now in engagement with its second hand contact, wiper 122, bank contact 132, terminal No. 3 on the right-hand side of the I. D. F. bank contact 175, wiper 162, through the winding of the stop relay 141 to battery. Relay 1.41 operates in the manner described above and performs circuit changes as described above, after which the sender switch SS is again returned to normal and the sequence switch wipers 102 and 103 are advanced into engagement with their'third set of bank contacts.

In response to the five circuit interruptions produced by the sender switch SS, rotary connector RC operates to-raise its wipers opposite the fifth level of bank contacts.

In a similar manner the sender switch SS operates and sends a third digit of six impulses to the rotary connector BC. The cir-.

cuit-for the stop relay 141 this time includes wiper 121, and bank contact 131 cross-connected to terminal No. 6 on the'right-hand side of the I. D. F. After sending the six impulses the sender switch SS is returned to normal and the sequence switch wipers 102 and 103 are advanced into engagement with their fourth set of bank contact-s.

In response to the six impulses of the last digit sent to the rotary connector BC, the connector RC rotates its wipers 72, 7 3, and 74 into engagement with the sixth set of bank contacts in the fifth level, this being the set of bank contacts in which the first trunk to the desired P. B. X. terminates. The rotary connector RC now performs its automatic rotary trunk huntingmovement to select an idle trunk to the desired P. B. X. in the well known manner.

When wiper 103 engages its fourth bank contact, a circuit is closed for the switching relay 104 of the trunk circuit TC which may be tracedfrom ground byway of wiper 103 and the fourth contact, impulse conductor 44, bank contact- 44 wiper 40, working contact and armature 34, armature 16 and the working contact, through the winding of the switching relay 14 to battery. Relay 14 operates and performs the following circuit changes:' At armature 23, another point in the circuit of the operating magnet 35 is opened. At armature 24 and the working contact, the circuit of the switching relay 30 is opened and at the working contact thereof, a locking circuit for the switching relay 14' is closed. At armature 25 ground potential is removed from bank contact 44 and its multiples and the circuit of the release relay 140 in the register sender is opened. At armatures 22 and 26 and their working contacts the talkingcircuit is extended to the succeeding switches, the circuit of the line relay 11 being opened at the resting contacts of these armatures and the control circuit being disconnected by the separation of the normally closed contacts controlled by these armatures. When the circuit of the line relay '11 is opened this relay deenergizes and restores its armatures to normal, opening the circuit of release relay 12 at armature 15. A short time after its circuit is opened, relay 12 restores its armatures to normal. Ground is maintained on release conductor 3, which is continuous through all the operated switches, by the release relay in rotary connectorRC.

IVhen the circuit of the release relay 140 is opened, this relay deenergizes and opens the locking circuit of the relay 107 by the disengagement of armature 144 with its working contact, and closes the circuit for the release magnet 119, which may be traced from ground by way of armature 144, now engag ing its resting contact, through the ofl:'normal springs 116 closed upon the first vertical step of the register wipers, through the winding of-the release magnet 119 to battery. Release magnet 119 operates and restores the wipers of the register R to normal in the well known manner. At armature 145 a self-interrupting stepping circuit for the sequence switch magnet 101 is closed which may be traced from ground byway of the resting contact and armature 145, conductor 143 multiply connected to all the contactsexcept the normal position contacts, wiper 102, interrupting springs 104 through the winding of magnet 101 to battery. Magnet 101 operates, moves the wipers 102 and 103 into another normal position, in this case, to bank contacts 102 and 103 respectively.

The register sender has now been restored to normal and may now be seized for operation in extending another call.

' After the rotary connector RC has seized tion is desired, the P. B. X. operator finally completes the desired connection.

The two subscribers may then engage in conversation, at the termination of which both subscribers will replace their receivers. Replacing the receiver at the called substation may operate a disconnect signal in the well known manner, wh reupon the P. B. X. operator will pull down the connection at her position. In response to the'replacement of the receiver at the calling substation, the bridge at the calling station across the talk ing conductors is opened thereby initiating the release of the rotary connector RC in the well known manner. In the rotary connector RC ground potential is removed from the release conductor which initiates the release of the preceding switches, including selector S and rotary lineswitch RLS. The

removal of ground from holding conductor 53 also opens the holding circuits of switchin relay 14 and of relay 13, whereupon these relays deenergize and restore their armatures to normal. The trunk terminating in bank contacts 2, 3 and l is now free and may be seized to extend another call.

From this description of the operation of this part of the above telephone system, it is evident how the above mentioned objects are accomplished. For example, should the number of trunks to the P. B. X. in question, now having five trunks accessible in the last five contacts in the fifth level of rotary connector group No. 3, be increased to ten, the present five trunks and the five additional trunks need merely be connected to any vacant level in the banks of any one of the three groups of connectors. The only other change necessary is the reconnection of the jumpers on the I. D. F. If this vacant level be the eighth level in the second group of connectors, the reconnections on the l. D. will be as follows: Wiper 133, will be cross-connected to right-hand terminal No. 2; wiper 132 will be cross-connected to righthand terminal N. 8 and wiper 131 will be cross-connected to right-hand terminal No. 1. Now when the telephone number 01: the P. B. X. in question is dialled by a calling subscriber, wipers 121, 122, and 123 of register R, assuming that the'rcgister sender shown in Fig. 2 is again taken for use, will again be positioned on bank contact 131, 132, and 133, respectively. The sender switch SS will now operate to send the digits 2. 8, and 1, consecutively, thereby causing the selector S to select an idle rotary connector in the second group of connectors, and causing this seclected rotary connector to position its wipers on the first set of contacts in the eighth level. The rotary connector then operates to select an idle one of the ten trunks extending to the PB. X. in question, after which the connection is completed, in the same manner as described above.

It is also evident that only a certain. one hundred consecutive numbers are necessary for the telephone numbers of one hundred P. B. X.s, each number being the designation of a P. B. X., and having no relation to the number of trunks to that P. B. X., or to their positions in the rotary connector banks, or the par icular group of rotary connectors in whose banks the trunks terminate. It is also evident that the telephone number of any P. B. X. may be, changed merely by changing the three jumper connections at the I. D. F., i. 'e., by connecting the left-hand ends of these three jumpers to the bank contact terminals corresponding to the last two numbers of the desired new telephone numher.

A more complete explanation of the manner and means provided for causing the second selector taken into use to select not only an idle trunk but such idle trunk whose associated register sender selector is positioned on the contacts leading to an idle register sender may now be given. Each trunk circuit, such as the trunk circuit TC, is provided with a relay, such as relay 13,. which is connected directly to the release conductor of the trunk with which it is associated. Thus each such relay will be energized when ground potential is present on the release conductor of the trunk with which it is-associated. Normally a metallic path extends from the release conductor of each trunk by way of the armature, suchas armature 25, and its resting contact to the test wiper of the associated register sender selector, such as wiper 39. Therefore, ground potential may be present on the release conductor by reason of the trunk being busy in a connection and applied thereto by the rotary connector in use in this connection, or may also, be present thereon by reason of theregister sencer accessible in the bank contacts on which the wiper of the associated register sender selector, such as wiper 39, is positioned, being busy. In the latter case,yground is applied to the bank contact, such as bank contact-a8, over a path by way or the armae ture similar to armature 17 of the release re lay of the trunk circuit associated at that time with the busy register sender, armature similar to armature 25, by way of wiper sin-- ilar to wiper 39, to the test contacts similar to and multipied with contact 43. Thus a trunk is guarded against seizure not only when it is busy in a connection, butvalso when it is idle and its associated register sender selector is positioned on-the contacts con nected to a busy register sender.

A chain circuit extends through the trunk circuits of each group of trunks. The operations are the same for each group of trunks, so only one group need be considered. In operating, each relay similar to the relay 13, closes a point'in the circuit of the operating magnet of the register sender selector wit-h which it is associated at an armature, such as armature 21, and also short circuits its associated resistance such as resistance 27 at an armature such as armature 20. These resistances are included in the chain circuit of the marginal relay 5. The circuit or" all the rotary magnets similar to rotary magnet 35 of the register sender selectors of this group is normally open at the armature 6. The marginal relay 5 is so adjusted that it will not operate unless all but two of the resistances such as resistances 27 and 2. are short-circuited. \Vhen all but two of these resistances are short-circuited, marginal relay 5 operates and applies battery to the common battery feed conductor 8 at armature 6, thereby closing a circuit-for all the rotary magnets such as magnet 35 of the register sender seill) lectors associated with trunks that are idle at thistime and whose wipers are positioned on the control conductors extending to busy register senders. The circuit of each rotary magnet is like that for magnet 35, which will extend from the common battery teed conductor 8 by way of resting contact and armature 23, working contact and armature 21, resting contact and armature 18, through the 10 winding of the rotary magnet 35, interrupter contacts 36, wiper 39, to the bank contact with which it is engaged and upon which ground potential will be present providing that the register sender accessible thereat is 5 busy at this time. The rotary magnets whose circuits are thus closed will operate and rotate the wipers of their register sender selector. As soon as one of these register sender selectors is rotated into engagement with the contacts to which an idle register sender is connected, the wiper, such as 39, no longer finds ground and the switch stops. At the same time the relay, such as relay 13, associated with the trunk circuit with which that 26 register sender selector is associated, will be deenergized thereby opening the circuit of the rotary magnet of that register sender selector at its armature similar to armature 21, and will also remove the short circuit around 30 the associated resistance such as resistance 27. The operation of the other register sender selectors may continue however until at least four resistances similar to resistance 27 are not short-cireuited. Vhen the short-circuit is removed from four resistances similar to resistance 27, marginal relay 5 will deenergize and remove ground from the common battery feed conductor 8. By the removal of battery from the battery feed conductor 8, the circuit of all the rotary magnets will be opened and the hunting operation of all register sender selectors so operated will cease. Therefore, in each group of trunks accessible in the banks of the second selectors in the P. B. X. level at least two of the idle trunks will always have their associated register selectors positioned on the control conductors leading to an idle register sender.

The invention, its features and the operation of the apparatus used having been described, what is considered new and desired to have protected by Letters Patent will be specifically stated in the appended claims.

What is claimed is: 1. In a telephone system, a plurality of private branch exchanges, said exchanges having assigned thereto consecutive telephone numbers. one for each exchange, a plurality of groups of rotary connectors, trunks accessible in the banks of said rotary connectors extending to said exchanges, means responsive to the dialing of acomplete telephone number for controlling the operation of a rotary connector to connect with a trunk 65 extending to the exchange corresponding to the telephone number dialed, and means whereby the position of said trunks in the banks of said rotary connectors may be changed from one level to another, and from one group of rotary connectors to another without attesting the telephone numbers of the corresponding exchanges.

2. In a telephone system, a group of rotary connectors, a plurality of private exchanges, said exchanges having assigned thereto consecutive complete telephone numbers, one for each exchange, a plurality of trunks extending to each exchange accessible in the banks of said rotary connectors, and means whereby the number of an exchange may be changed Without affecting the position of trunks in the banks of said rotary connectors.

3. In a telephone system, a group of rotary connectors, a plurality of private exchanges, said exchanges having assigned thereto con secutive complete telephone numbers, one

for each exchange, a plurality of trunks extending to each exchange accessible in the banks of said rotary connectors, and means whereby the position of the trunks in the banks of said rotary connectors may be changed without afi'ecting the telephone number of anyexchange.

4. In a telephone system, rotary connectors, groups of trunk lines terminating in the banks of said connectors, said trunk groups being assigned consecutive complete telephone numbers, and means responsive to the calling of any number for directing one of said connectors to the corresponding group of trunk lines. V v

5. In a telephone system, a plurality of private exchanges, said exchanges having assigned thereto, consecutive telephone numbers, one for each exchange, a'group of rotary connectors. a plurality of trunks extending to each exchange accessible in the banks of said rotary connectors, a line, means for extending a connection from said line to an idle rotary connector, a register, means responsive to the sending of the first digits of a desired telephone number for extending a connection to the register, means for sending impulses corresponding to the remaining digits ofthe desired telephone num-, ber oversaid line to said register, and a sender under the control of said register for sending other impulses to control said first means and for controlling the operation of the selected rotary connector.

6. In a telephone system, outgoing lines extending to an exchange, rotary connectors having access to said outgoing lines, a selector having access to said connectors, a trunk line, a register sender associated with said trunk line, means for sending the last two digits in a telephone number over said trunk line to.

said register sender, and means in said register sender for translating said digits into other d1gits and for sending said other digits over said trunk to operate said Selector to connect with an idle connector and to operate said connector to connect with an idle trunk line. Y

7 In a telephone system, an automatic switch, a plurality of trunks accessiblein the banks of said automatic switch, a register sender selector associated with each. otsaid trunks, each selector having sets of bank contacts and wipers adapted to engage said sets consecutively and always in engagement with a set oi'contacts, a register sender connected to each of said sets of contacts, means'fo'r causing said automatic switch to perform an idle trunk hunting movement, and means associated with each trunk whereby said automatic switch is capable of selecting only such idle trunk whose associated register sender selector is connected with an idle register sender.

8. In an automatic telephone system wherethe class indicating digit for determining whether the subsequent digit impulses, shall be transmitted direct or by way of the register sender, and means in the register sender for transmitting more groups of digit impulses than are received.

9. In an automatic telephone system wherein the establishment of connections is controlled by groups of digit impulses, lines of two classes, the class of any particular line being indicated by an intermediate digit of the telephone number of the line, a register sender, means controlled by the impulses of the class indicating digit for determining whether the subsequent digit impulses shall be transmitted direct or by way of the register sender, means in the register sender for transmitting more groups of digit impulses than are received, means in the register sender for changing at will the value of the digits transmitted corresponding to any particular series of digits received.

10. In an automatic telephone system wherein connections between parties are established by means of series connected automatically operated switches, lines of two classes, the classification of the lines being indicated by an intermediate digit of the telephone numbers of the lines, a coding apparatus, means responsive to the dialling of the class indicating digit for extending'a call to the coding apparatus or to a connector, depending upon the value of the dlglt, means in the coding apparatus effect1ve 11 the coding apparatus is selected for receiving and retransmitting in code the subsequent digit impulses representing the desired number, and means for altering the code at w1ll.

11. In atelephone system wherein conneci ns betw en all g and ca d part esa e established by means including seriesconnected, automatically operated switches, each operated in accordance with a series of digit mpu ses eceiv d by t, odi g app r t interposed between the last switch of the series and a preceding switch, said p a us inc g ans er t ansmi ti o he l t itch o the es se i of impulses corresponding to the series of impulses received, and means for altering the code a Will. i

2- In a t lep n sy m wher in 1. nections between calling and called parties are established by means including series connected, automatically operated switches, each operated in accordance with a series of mpu ses r c y t in appara u interposed between the last switch of the series and a preceding switch, said coding I apparatus including meansfor receiving and retransmittlng in code the serles ofimpu-lses for operating all of the subsequent switches,

and means whereby the code corresponding any o th series imp l e r ansmitted may be changed at will.

3- I a i m t tale be i sys wh re a r tat li ea en as masthseribers station terminates in a connector nd s a c ssi le by ia ine a ce n mutiber, means whereby the las t two the complete telephone number be changed at will while maintaining the ,p si: tion at which the terminates in cennector the same. 4 l 14. 'In a telephone system a .plur ality' e t trunks "each "having a selecting lassoei t'd wi lur l yb re i e se ers accessible to, said selecting sw itche said e ect sw t hes hang a eessent a with some register sender, efiegn e when the ,reg istersendergwith a said eh is associated becomes busy 'forin" l'n' artificial busy condition of ,the trunli wit which ,the switq h is associated, antl' ,m'ea, s elijective when predetermined number of was 'e 't t ifi e 'ltet asfbin t ar ssa" s e es el eeso i te wi h i we m kes stea t? be associated with erent reg ster senders.

a e t m ma net i R trunks each .having'a selecting switch ,a ss ociated therewith',a zpl'urality o f register se de sv ae si t5 d ti e sate-e d selecting switches being lliva'ys' assoe gtefd with sam register seed r w s tie te tis? e t L ch s n est ime th ic le eseas and Futi e-t e selQiie as e se lat d wit tl e mel a ma a e wit be t r is sweeteners 'sfieeti et er lL- et .e' tedet us nsiemeb i a name are marked busy for causingithe selecting uite-he asse ie ed wi h ae t lieae dhee thbs iirssi ee is to @,-paa t find idle register senders until a predetermined number of trunks are free from the I trunks each having a selectlng switch associated therewith, each selecting switch having a plurality of contacts any'of which may bein a selectable or non-selectable condition, each selecting switch always being associated with some one of its contacts, means for marking each trunk busy whenever the trunk is engaged and whenever the associated selecting switch is associated with a contact in a non-selectable condition, means eifective under certain conditions for causing the selecting switches associated with the non-engaged trunks and with non-selectable contacts to operate to find selectable contacts until less than a predetermined number of trunks are marked busy.

17. In a an automatic telephone system whereinthe establishment of connections is controlled by groups of digit impulses, lines istering switch in accordance with the last digit-of a called subscribers telephone number,' a sender controlled'by said register to send out a plurality of digits of different respective values in accordance with the setting of said registeringswitch, and means whereby the value ofthe digit sent out in response to a given register setting may be readily ting of the register, for disassociating sai director from said trunk line. V In witness whereof, I hereunto subscribe my name this 5th day of April, A. D., 1926.

RODNEY e. RICHARDSON.

changes, each exchange having a complete telephone number assigned thereto, an automatic switch, trunk groups terminating in the banks of said switch'and extending to said exchanges, respectively, means for operating said switch to extend a connection to any one of said exchanges, and means whereby the position of the trunk groups in the banks of'said switch may be interchanged without affecting the telephone number of any exchange.

19. In a telephone system, subscribers lines, each line having a complete telephone number assigned thereto, an automatic switch terminating said lines in its banks, means for operating said switch to connect with either line, and means whereby the telephone numbers assigned to said lines may be interchanged without changing the position of said lines in the banks of said switch.

20. In a telephone system, a two-motion register switch having a single set of wipers, means for setting said wipers in accordance with the last two digits ofa called subscribers number, a sender controlled by said switch in accordance with its wiper setting to control the establishment of the connection to the called subscriber, and translating means interposed between the register switch and the sender.

21. In a. telephone system, a multi-position registering switch, means for setting said reg- 

